In the conventional slim electronic apparatus as shown in FIG. 8, printed wired assembly substrates 3 (hereinafter referred to as PWAs) are placed. On the PWAs, heat generating components 2 such as semiconductors and a CPU are mounted. The heat generated from components 2 travels through heat conductive member 6 such as an aluminum plate, and is discharged outside the apparatus. The discharged heat amount is calculated with the following expression. EQU Q out .varies. .SIGMA.(Tsi-Ta) .times.Si
where:
Q out=discharged heat amount PA1 Tsi=a temperature at an "i" th cell of the housing surface, which is finely divided into cells PA1 Si=an area of the "i" th cell PA1 Ta=outer temperature PA1 Reduction of dimension "a": decreasing the motor power and lowering the motor efficiency; PA1 Reduction of dimension "b": decreasing the air volume; and PA1 Reduction of dimension "c": degrading the strength of the frame; and weakening the heat sink function, PA1 (a) PWAs including heat-generating electronic components such as semiconductors, and being disposed in a housing of a thin-type electronic apparatus, such as a mobile personal computer or a digital video camera, so that a given space is provided between the housing and the PWAs; PA1 (b) a cooling fan motor having a small and tubular case made of heat-conductive materials such as copper, aluminum and the like, the cooling fan motor having a height smaller than the height of the housing, and being disposed in the given space provided in the housing; and PA1 (c) an air discharge opening through which the heated air in the housing is discharged.
Accordingly, the housing temperature rises and an area of high temperature increases as greater built-up heat amounts are produced by the components.
When this structure is employed in an electronic apparatus such as a mobile computer or a digital video camera, the interior built-up heat could potentially damage its internal electronic operating components. Further, since these apparatus are held by a user's hand during operation, the temperature rise on the housing surface makes the user uncomfortable. Therefore, it has been proposed to discharge the interior built-up heat forcibly outside the apparatus by providing a cooling fan in the apparatus.
In the prior art depicted in FIGS. 9A and 9B, components 2 that generate heat, such as semiconductors, are mounted on a PWA 3 that is installed in housing 1. On one of inside faces of housing 1, cooling fan 5 is provided. The height of fan 5 is substantially equal to that of a housing 1 and frame 4 of fan 5 functions as a heat sink. The heat produced by components 2 travels to fan 5 via heat conductive member 6 made of e.g. aluminum. Then fan 5 drives blades 7 to forcibly discharge the heat outside the apparatus.
FIG. 10 is a cross section of an essential part of another electronic apparatus with a conventional cooling fan. In FIG. 10, a plurality of PWAs accommodating heat generating components 2 such as semiconductors are installed in the housing 1. PWA 3 installed at the lowest place in housing 1 is shortened at its end in order to provide a space between PWA 3 and a side of the housing. In this space, flat cooling fan 8 is disposed so that its shortest side extends in the height direction of the apparatus. The frame of fan 8 functions as a heat sink. The heat produced by components 2 travels to fan 8 via heat conductive member 6 made of e.g. aluminum. Then fan 8 forcibly discharges the heat outside the apparatus. The structure in FIG. 10 mentioned above is employed in a large number of slim notebook-type personal computers. In addition to ensuring reliability of the personal computers, it is desirable that the height of cooling fan 8 be as low as ca. 7.5 mm so that the total housing height of the apparatus should be less than 20 mm.
The structure in FIG. 9 is compared with that in FIG. 10 to find the following fact. The structure in FIG. 9 can be employed in the electronic apparatuses such as notebook type personal computer of which total height ranges from 25 to 40 mm. However, in the case of mobile computers requiring a further compact and slim body, the height of cooling fan 5, i.e. 2 .times.(a+b+c) becomes a possible obstacle to meeting requirements.
where "a"=radius of motor, "b"=blade height, "c"=frame thickness
The height of an electronic apparatus that requires an extra slim body is often restricted by the height of cooling fan 5. In order to reduce the height of fan 5, each dimension mentioned above, i.e. "a", "b" and "c" should be reduced; however, the following inconveniences accompany this reduction:
The height of cooling fan 5 is thus cannot readily lowered, which has been an obstacle to further downsizing of compact electronic apparatuses such as mobile personal computers.
The structure shown in FIG. 10 has been proposed to overcome the problem of the structure shown in FIG. 9. However, in the case of compact electronic apparatuses such as a mobile personal computers this structure of FIG. 10 still has the following problem. Two sheets of double sided PWA accommodate the components. Assume that each PWA measures 50 mm.times.100mm Then the total components-mounting-area is thus 50 mm.times.100 mm.times.2 sides.times.2 sheets=20000 mm.sup.2.
In order to dispose a fan 8 that measures 40 mm.times.40 mm, one PWA 3 should be cut out, which reduces the components-mounting-area by 40 1mm.times.40 mm.times.2 sides=3200 mm.sup.2. As a result, the total components-mounting-area is reduced by 16%.
This area-reduction decreases the number of components which can be mounted, and has been an obstacle to realizing compact size electronic apparatus having high performance and versatile functions.